Method and apparatus for improving resist pattern developing

ABSTRACT

An apparatus and method for developing a selectively exposed resist pattern, on an integrated circuit wafer, which avoids damage to the resist pattern and allows greater freedom in the choice of resists. Developer is placed on a selectively exposed layer of resist for a first time. The layer of resist and developer are then immersed in a cleaning liquid time for a second time to stop the developing action and remove the developer. As an option, ultrasonic power can be delivered to the wafer or the cleaning liquid while the layer of resist is immersed in the cleaning liquid. The cleaning liquid is then removed from the layer of resist, now a resist pattern, and the wafer and resist pattern is placed in a vacuum for drying. As another option, heat can be applied to the wafer and resist pattern while they are in the vacuum. The wafer and resist pattern are then removed from the vacuum for further processing.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] This invention is related to the developing of a selectivelyexposed layer of resist formed on an integrated circuit wafer and moreparticularly to stopping the developing process and removing the resistusing immersion in de-ionized water followed by a vacuum dry period. Thevacuum dry period may also include heating the wafer using a heat lamp.

[0003] (2) Description of the Related Art

[0004] U.S. Pat. No. 4,902,608 to Lamb et al. and U.S. Pat. No.5,025,280 to Lamb et al. describes a method and apparatus for immersinga selectively exposed layer of photoresist on a wafer first in a bath ofdeveloper and next in a bath of de-ionized water. While the wafer is inthe de-ionized water it is slowly turned in the water. The wafer is thenremoved from the water and rapidly spun to spin dry the wafer andphotoresist.

[0005] U.S. Pat. No. 4,982,215 to Matsuoka describes a developingprocess where a workpiece having a resist layer is immersed in a bath ofdeveloper at a first temperature. Electrical current between theworkpiece and an electrode also immersed in the developer to monitor theprogress of the developing process. When the developing process has beencompleted an additional amount of developer at a second temperature,lower than the first temperature, is added to the original developer asthe withdrawl of the developer is begun. The progress of the developmentis thus retarded providing precision for the endpoint of the developmentprocess.

[0006] This invention describes a method and apparatus for developing aresist pattern that does not require spinning the wafer and does notrequire batches of developer at different temperatures.

SUMMARY OF THE INVENTION

[0007] Resist patterns are routinely used in the manufacture ofintegrated circuit wafers. These resist patterns are formed byselectively exposing a layer of resist, using photolithography orelectron beam methods or the like, and developing the selectivelyexposed layer of resist to form the pattern. Developing the resist iscarried out by placing the exposed resist in contact with liquiddeveloper material for a certain time followed by washing the developeraway with de-ionized water, or other cleaning liquid. The de-ionizedwater is then removed by drying the resist pattern.

[0008] As the level of integration of integrated circuits increasesproblems are encountered with the conventional method of developingresist patterns. Some of the problems encountered developing resistpatterns will be described with reference to FIGS. 1-3. FIG. 1 shows thetop view of an integrated circuit wafer with a layer of selectivelyexposed resist formed thereon and liquid developer material placed onthe layer of selectively exposed resist 10. FIG. 2 shows a cross sectionview of the integrated circuit wafer of along the line 2-2′ of FIG. 1.FIG. 2 shows the integrated circuit wafer 12 placed on a wafer holder18. The layer of selectively exposed resist 14 is formed on theintegrated circuit wafer 12. Liquid developer material 16 is placed onthe layer of resist 14. The wafer holder 18 is attached to a shaft 20.

[0009]FIG. 3 shows a cross section view of the integrated circuit waferafter the developing of the exposed resist has been completed. The layerof resist has been developed forming a resist pattern 15. The shaft 20attached to the wafer holder 18 is attached to a means 22 for spinningthe shaft 20, wafer holder 18, integrated circuit wafer 12, anddeveloped resist pattern 15 as indicated by the rotational arrow 36. Asthe spinning of the wafer begins, and is still at a low speed, valves 27and 29 are opened and de-ionized water is fed from a de-ionized watersupply 26 through a pipe 28 to nozzles 30 which spray de-ionized wateron the developed resist pattern 15 forming a layer of deionized water 24over the resist pattern. De-ionized water is also directed from thede-ionized water supply 26 through a pipe 32 to a nozzle 34 to sprayde-ionized water on the back side of the wafer. The valves 27 and 29 arethen closed stopping the supply of de-ionized water to the integratedcircuit wafer. The wafer is then spun at high speed to dry the wafer,thereby removing any residual de-ionized water. In this conventionaldeveloping method the de-ionized water, or other cleaning liquid,imparts a force to the fine elements of the resist pattern as the waferis spun at high speeds often damaging the resist pattern.

[0010] It is a principle objective of this invention to provide a methodof developing and cleaning a layer of selectively exposed resist whichwill avoid damage to the developed resist pattern.

[0011] It is another principle objective of this invention to provide anapparatus for developing and cleaning a layer of selectively exposedresist which will avoid damage to the developed resist pattern.

[0012] These objectives are achieved by immersing the integrated circuitwafer with developer on the resist pattern in de-ionized water afterdeveloping the resist pattern has been completed. There is no spinningof the wafer however low levels of ultrasonic power may be used. Thewafer is then removed from the de-ionized water and the chambercontaining the wafer is evacuated, using a means such as a vacuum pump,to dry the wafer. Heat, using a means such as a heating lamp, may beapplied to the wafer while the chamber is evacuated. During thedeveloping process no force is exerted on the resist pattern by thecleaning liquid, damage to the pattern is avoided, and a wider choice ofresists is available.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 shows a top view of an integrated circuit wafer with alayer of selectively exposed resist and developer placed on the resist.

[0014]FIG. 2 shows a cross section view of an integrated circuit waferwith a layer of selectively exposed resist and developer is placed onthe resist. The wafer is attached to a wafer holder and the wafer holderis attached to a shaft for spinning the wafer.

[0015]FIG. 3 shows a schematic cross section view of an apparatus for aconventional method of cleaning the developer from the developed layerof exposed resist using de-ionized water and spinning the wafer at highspeeds.

[0016]FIG. 4 shows a schematic cross section view of the apparatus andmethod of this invention showing the wafer placed in a chamber anddeveloper placed on the selectively exposed layer of resist.

[0017]FIG. 5 shows a schematic cross section view of the apparatus andmethod of this invention showing the wafer placed in a sealed chamberand the wafer and the developed layer of resist immersed in de-ionizedwater.

[0018]FIG. 6 shows a schematic cross section view of the apparatus andmethod of this invention showing the wafer placed in a sealed andevacuated chamber after the de-ionized water has been removed from thechamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The apparatus of this invention used for developing a selectivelyexposed layer of photoresist will now be described in detail withreference to FIGS. 4-6 which show a cross section view of the apparatus.Like reference numbers are used for like components in FIGS. 4-6. Asshown in FIGS. 4-6 a first end of a first shaft 20 passes through avacuum tight seal 50 in the bottom 49 of a chamber 51 and is attached toa wafer holder 18 inside the chamber 51. The second end of the firstshaft 20 is attached to a means 23 for delivering ultrasonic power tothe wafer holder 18. The integrated circuit wafer 12 is attached to thewafer holder 18. The chamber 51 is formed of a material such as quartzor metal with a coating to prevent metal contamination.

[0020] A first vacuum tube 46 passes through a port in the sidewall 48of the chamber 51 and is connected to a vacuum valve 44. A second vacuumtube 42 is connected between a vacuum pump 40 and a the vacuum valve 44so that the vacuum pump 40 can evacuate the chamber. A first exhausttube 76 passes through a port in the sidewall 48 of the chamber 51 to anexhaust valve 74. A second exhaust tube 72 connects the exhaust valve 74to an exhaust reservoir 70 for collecting and disposing of exhaustgasses. A first liquid tube 66 passes through a port in the sidewall 48of the chamber 51 to a liquid valve 64. A second liquid tube 62 connectsthe liquid valve 64 to a cleaning liquid supply 60, such as a de-ionizedwater supply. A first drain tube 80 passes through a port in the bottom49 of the chamber 51 to a drain valve 82. A second drain tube 84connects the drain valve 82 to a drain reservoir 86 for collecting anddisposing of liquids drained from the chamber 51.

[0021] As shown in FIGS. 5 and 6, a removable top 92 is placed on thechamber 51 and a vacuum gasket 96 provides a vacuum seal between thesidewalls 48 of the chamber and the removable top 92. A heating element94, such as a heating lamp, is attached to the removable top 92 and canprovide heat energy to the integrated circuit wafer 12. As shown in FIG.5, de-ionized water 90 delivered from the de-ionized water source 60through the second liquid tube 62, the liquid valve 64, and the firstliquid tube 66 can fill the chamber 51 to a sufficient height to immersethe integrated circuit wafer 12 in de-ionized water. The first draintube 80, the drain valve 82, and the second drain tube 84 can drain thede-ionized water from the chamber 51 to the liquid reservoir 86, asshown in FIG. 6. The first end of an optional second shaft 120 can beconnected to a means 123 to deliver ultrasonic power directly to thecleaning liquid. The second end of the second shaft 120 then passesthrough a vacuum seal 150 in the bottom 49 of the chamber and isconnected to a transducer 100 in the cleaning liquid.

[0022] Refer now to FIGS. 4-6 for a description of the preferredembodiment of the method of this invention for developing and cleaning aselectively exposed layer of resist. As shown in FIG. 4 an integratedcircuit wafer 12, having devices formed therein and a selectivelyexposed layer of resist 14 formed thereon, is placed on a wafer holder18 in the chamber 51. The layer of resist 14 can be photoresistselectively exposed using photolithographic methods, resist selectivelyexposed using electron beam methods, or the like. Developer 16 is placedon the layer of selectively exposed resist 14 to begin the developingprocess. As shown in FIG. 5, the top 92 of the chamber is then placed onthe sidewalls 48 of the chamber and the vacuum gasket 96 seals the top92 to the sidewalls 48.

[0023] After the developer has been in contact with the selectivelyexposed layer of resist for a first time, between about 0.5 and 2.0minutes, a resist pattern 15 is formed from the selectively exposedlayer of resist. The vacuum valve 44 and the drain valve 82 are closed.The exhaust valve 74 is opened, allowing gas to escape from the chamberthrough the first exhaust tube 76 and the second exhaust tube 72 to theexhaust reservoir 70, and the liquid valve 64 is opened, allowingde-ionized water from the de-ionized water supply 60 to flow through thesecond liquid tube 64 and the first liquid tube 66 into the chamberuntil the resist pattern 15 is immersed in de-ionized water 90, see FIG.5.

[0024] During the time the resist pattern 15 is immersed in thede-ionized water a first ultrasonic power source 23, connected to ashaft 20 which is also connected to the wafer holder 18, can deliverultrasonic power to the integrated circuit wafer 12 to aid in theremoval of residual developer. As an optional alternative a secondultrasonic power source 123, connected to a shaft 120 which is alsoconnected to a transducer 100 immersed in the de-ionized water 90, candeliver ultrasonic power to the de-ionized water 90 to aid in theremoval of residual developer.

[0025] After the resist pattern 12 has been immersed in the de-ionizedwater for a second time the drain valve 82 is opened and the de-ionizedwater is drained through the first drain tube 80 and the second draintube 84 into the drain reservoir 86, as shown in FIG. 6. The drain valve82, the liquid valve 64, and the exhaust valve 76 are closed. The vacuumvalve 44 is then opened and the vacuum pump 40 maintains a pressure inthe chamber of about 1×10⁻² Torr or lower for between about 0.5 and 2.0minutes. As an option the heat source 94, for example a heat lamp, canbe used to elevate the temperature of the integrated circuit wafer 12and resist pattern 15 to a temperature of between about 90° C. and 120°C. during the period the chamber is evacuated.

[0026] The vacuum valve 44 is then closed, the exhaust valve 74 isopened to equalize the pressure in the chamber, and the top 92 isremoved from the chamber. The integrated circuit wafer 12 with thecompleted resist pattern 14 is then removed from the wafer holder 18 andthe chamber 51 for further processing. During the developing processdescribed there has been no force exerted on the resist pattern by thecleaning liquid and damage to the pattern is avoided.

[0027] This example has used a single cleaning liquid, in this examplede-ionized water, to stop the developing process and clean the developerfrom the wafer. As an alternative other liquids or more than onecleaning liquid can be used. In this embodiment the integrated circuitwafer 12 and resist pattern 14 are first immersed in a first cleaningliquid, for example a surface agent such as de-ionized water. The firstliquid is then drained and the integrated circuit wafer 12 and resistpattern 14 are immersed in a second cleaning liquid, for examplede-ionized water. The second cleaning liquid is then drained and theembodiment proceeds as in the preceding embodiment after the de-ionizedwater has been drained.

[0028] While the invention has been particularly shown and describedwith reference to the preferred embodiments thereof, it will beunderstood by those skilled in the art that various changes in form anddetails may be made without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A method of forming resist patterns, comprisingthe steps of: providing an integrated circuit wafer; forming a layer ofresist on said integrated circuit wafer; selectively exposing said layerof resist; placing developer on said selectively exposed layer ofresist; immersing said integrated circuit wafer in a bath of cleaningliquid after said developer has been placed on said selectively exposedlayer of resist for a first time; removing said integrated circuit waferfrom said bath of cleaning liquid after said integrated circuit waferhas been immersed in said bath of cleaning liquid for a second time; andremoving residual said cleaning liquid from said integrated circuitwafer.
 2. The method of claim 1 wherein said cleaning liquid isde-ionized water.
 3. The method of claim 1 further comprising immersingsaid integrated circuit wafer in a surface agent prior to said immersingsaid integrated circuit wafer in said cleaning liquid.
 4. The method ofclaim 1 wherein said resist is photoresist and said selectively exposingsaid layer of resist uses photolithographic processing.
 5. The method ofclaim 1 wherein said selectively exposing said layer of resist uses anelectron beam.
 6. The method of claim 1 wherein said removing residualsaid cleaning liquid from said integrated circuit wafer comprisesplacing said integrated circuit wafer in a vacuum wherein the pressureis less than 1×10⁻² Torr.
 7. The method of claim 6 wherein said removingresidual said cleaning liquid further comprises heating said integratedcircuit wafer.
 8. The method of claim 1 further comprising applyingultrasonic energy to said integrated circuit wafer while said integratedcircuit wafer is immersed in said bath of said cleaning liquid.
 9. Themethod of claim 1 further comprising applying ultrasonic energy to saidcleaning liquid while said integrated circuit wafer is immersed in saidbath of said cleaning liquid.
 10. A method of forming resist patterns,comprising the steps of: providing an integrated circuit wafer; forminga layer of resist on said integrated circuit wafer; selectively exposingsaid layer of resist; placing said integrated circuit wafer in achamber; placing developer on said selectively exposed layer of resistafter said integrated circuit wafer has been placed in said chamber;placing cleaning liquid in said chamber thereby immersing saidintegrated circuit wafer in said cleaning liquid after said developerhas been placed on said selectively exposed layer of resist for a firsttime; removing said cleaning liquid from said chamber after saidintegrated circuit wafer has been immersed in said cleaning liquid for asecond time; sealing said chamber; evacuating said sealed chamber to apressure of about 1×10⁻² Torr or less after removing said cleaningliquid from said chamber; and opening said sealed chamber and removingsaid integrated circuit wafer after said integrated circuit wafer hasbeen in said sealed chamber at a pressure of about 1×10⁻² Torr or lessfor a second time.
 11. The method of claim 10 wherein said cleaningliquid is de-ionized water.
 12. The method of claim 10 furthercomprising placing a surface agent in said chamber thereby immersingsaid integrated circuit wafer in said surface agent, after saiddeveloper has been placed on said selectively exposed layer of resistfor a first time and before placing said cleaning liquid in saidchamber, and removing said surface agent from said chamber after saidintegrated circuit wafer has been immersed in said surface agent for athird time.
 13. The method of claim 10 wherein said resist isphotoresist and said selectively exposing said layer of resist usesphotolithographic processing.
 14. The method of claim 10 wherein saidselectively exposing said layer of resist uses an electron beam.
 15. Themethod of claim 10 further comprising heating said integrated circuitwafer after evacuating said sealed chamber to a pressure of about 1×10⁻²Torr or less and before opening said sealed chamber.
 16. The method ofclaim 10 further comprising applying ultrasonic energy to saidintegrated circuit wafer while said integrated circuit wafer is immersedin said cleaning liquid.
 17. The method of claim 10 further comprisingapplying ultrasonic energy to said cleaning liquid while said integratedcircuit wafer is immersed in said cleaning liquid.
 18. An apparatus forforming resist patterns, comprising: a chamber having sidewalls, abottom, and an open top; a chamber cover which can be placed on saidopen top of said chamber thereby sealing said chamber; an integratedcircuit holder extending through a vacuum seal in the bottom of saidchamber into the interior of said chamber; means for placing cleaningliquid into said chamber; means for removing said cleaning liquid fromsaid chamber; and means evacuating said sealed chamber to a pressure ofabout 1×10⁻² Torr or less.
 19. The apparatus of claim 18 furthercomprising a heating element attached to said chamber cover wherein saidheating element is inside said chamber when said chamber cover is placedon said open top of said chamber.
 20. The apparatus of claim 18 furthercomprising means for supplying ultrasonic power to said integratedcircuit holder.
 21. The apparatus of claim 18 further comprising meansfor supplying ultrasonic power to said cleaning liquid when saidcleaning liquid is placed in said chamber.
 22. The apparatus of claim 18wherein said means for evacuating said sealed chamber to a pressure ofabout 1×10⁻² Torr or less is a vacuum pump.
 23. The apparatus of claim18 wherein said cleaning liquid is de-ionized water.
 24. The apparatusof claim 19 wherein said heating element is a heating lamp.